1. Field of the Invention
The present invention relates to a process for applying water-based products, in particular water-based paints and/or varnishes, to the surface of glass articles. This process makes it possible to obtain various appearances such as an appearance of coloration in the bulk of the glass, a chemical satin-effect appearance or an enameled appearance. It is intended in particular for decorating jars, flasks, bottles or carafes of any type.
2. Discussion of the Related Art
The standard processes for applying varnish to glass articles consist in spraying the products onto their walls using a more or less complex array of pneumatic spray guns. However, the use of these processes involves many problems, and the results obtained are not satisfactory.
The deposition yields are generally less than 50%. These yields are proportionately lower the more complex the shape of the articles, this shape determining the number of spray guns required to obtain a homogeneous deposit on the surface of the articles. However, the larger the number of spray guns, the more complex it is to adjust the parameters relating to these spray guns in a manufacturing unit. In point of fact, these adjustments can last several hours, and it is necessary to remember not only the spatial position of each of the spray guns, but also their operating characteristics (air pressure for spraying, product pressure, nozzle diameter, horn pressure, type of cap, etc.) in order to ensure good reproducibility of the processes over time.
Despite the large number of spray guns which can be used and the tiresome adjustments which need to be carried out, the shape of certain articles is such that there are areas in which it is still difficult, or even impossible, for the sprayed product to reach.
Moreover, a homogeneous deposit of water-based paints and/or varnishes, containing very fine particles of resin in suspension in water, is particularly difficult to make. Water is in particular a solvent which is very difficult to spray, and pneumatic spray guns do not manage to disperse particles of homogeneous size. The particles ejected by the spray guns are, in point of fact, coarse in the axis of projection and increasingly fine on either side of this axis. This size disparity of the product particles has the consequence of giving rise to phenomena which interfere with the production of a high-quality deposit. Thus, the finest particles of varnish have a tendency to dry before reaching the glass substrate, or even of drying too quickly on this substrate, which gives rise to localized powdering, spattering and pitting effects on the surface of the treated articles. On the other hand, the coarsest particles of varnish are slow to dry after being sprayed on the surface of the articles, so much so that orange-peel effects, running and local excess thicknesses appear, which thus degrade the quality of the coating on the treated articles.
A first solution for overcoming all of these drawbacks consists in increasing the spraying air pressure excessively. However, this solution cannot be considered seriously since it does not allow the quality of the coating to be improved significantly and it also involves a considerable reduction in the spraying yield, which is, however, already very low.